More and more machines are connected to the Internet and machine-to-machine (M2M) communication requirements are expected to grow rapidly. M2M communications may also be referred to as D2D communications. The number of machines connected to the Internet in the near future is projected to be in the billions. Many of these communication requirements are covered if D2D communications (of devices close to each other) is facilitated. Existing proposals for D2D include using a different frequency band (e.g., 12 Ghz), using power line carrier communications, using WiFi-like systems (sense and use the same protocol), using cellular frequencies as secondary users with cognitive capability, and D2D facilitated by the approval of cellular network using an uplink depending on the situation and availability (e.g., Direct User Equipment (UE)).
With respect to the sharing of spectrum, currently a number of devices are sharing the industrial, scientific and medical (ISM) band. In some cases such as WiFi, listen before talk courtesy is being practiced (e.g., variants of carrier sense multiple access (CSMA) protocol). However, most machine to machine communications traffic typically is short packets, and in some cases may require some quality of service (QoS).
With respect to cognitive systems as secondary users, a spectrum owned by a primary user (e.g., a TV broadcaster) may be used by secondary users subject to some rules. Typically, the secondary user is required to sense the channel, and, if the signal of a primary user is present, refrain from transmission. Additional protection for the primary network also can be provided by: banning secondary transmissions in some bands in certain geographical regions, requiring access to a database to check for active primary transmitters in a region, refraining from transmission in their band, imposing strict limitations on transmission power of secondary devices, requiring the checking for beacons transmitted by the primary transmitter devices to determine if they are active, and the like.